Bleaching of cellulosic textiles



Patented Sept. 5, 1950 I BLEAcHING F CELLULOSIC TEXTILES.

Ralph L.Carr, Jackson Height's,'N. Y., assign'or to Mathieson Chemical Corporation, a. corporatio of Virginia This: invention relates to the treatment of cellulosic textiles. 'It relates more particularly tofimprovements in the treatment of such mate'- rialswitha chlorite, sodium chlorite'and calcium ch'lorite, for instance.

It has'heret'ofore been proposed to treat cellulosicjtxtiles; gray cloth, for instance, with an aqueous solution of achlorite for the purpose of bleaching or otherwise rei noving impurities therefrom, and it is recognized that the chlorites arefvaluable agents for such purposes. It is known, however, that the chlorites are relatively ina tive'fin neutral or alkaline solutions, but it has been found that thechlorites may be activja'tedby an acid conditioner. by the presence of certain other materials. l v

Sodium hypochlorite has been found to be a particularly desirable agent for activating the chlo'r'ite and accelerating the bleaching of the textile; Sodium hypochlorite alone has previously been used-in the bleaching of cellulosic textiles, but when so used has been found to attackthe' cellulosic fibers with a re'sultantten dering of the textile material. It has been found, however, that considerable proportions of sodium hypochlorite may be used in conjunction with sodium chlorite, for instance, without deleteriously affecting the textile. For example, cellulosic textiles have been satisfactorily bleached by treatment with an aqueous solution, of sodium 'hypochlorite and sodium chlorite, in which the ratio of hypochlorite to chlorite, on the basis of available chlorine, was about l /2:1. Such operations have been carried out successfully by treating th textile in an aqueous bath of the hypochlorite-chlorite solution at temperatures 1 ranging upwardly from about room temperature to somewhat less than 100 F. v v

It has'beenrecognized as desirable further to increase the treating temperature in order to 40 speed up the reaction; but it has been found that where the temperature of the'bath is increased to about 100 to 110 F. or higher, the hypochlorite constituent of the solution is rapidly decomposed in the presence of the chlorite, resulting in the relatively rapid evolution of chlorine dioxide, and the exhaustion of the hypochlorite constituent, with a minimizing of any advantages which might otherwise be obtained by increasing the treating temperature.

My present invention provides means'whereby cellulosic textiles may be treated with an aqueous solution of chlorite and hy-pochlorite at temperatures materially greater than heretofore found practical in 'such treatment, at a greatly No Drawing. Application May s, 1945, 4

Serial No. 594,164

' 4 Claims. (01. 8-108) 2 I. V 1 increased bleaching rate and without the disad' vantages heretofore experienced when attempting to operate at elevated temperatures.

In general, the process of any present invention comprises the impregnation of thetextile to be treated with an aqueous solutionof the chlorite and hypochlorite, and thereafter steaming the impregnated textile in the absence 'of surplus solution. I have found that under such conditiona'the hypochlorite is not rapidly decomposed in'the presence of the chlorite, the evolution of chlorine dioxide is substantially inhibited, and the textile is rapidly bleachedwith out deleterious eflects.

I recognize that it has previously beenproposed to steam textiles while. impregnated with "solutions of various reagents. However, so'far as I am aware, no one has heretofore proposed the subjecting of a textile impregnated with a hypochlorite-chlorite solution to the action of steam. The results obtained using this solution as a bath, in which the textile is submerged, when attempts Weremade to increase the operating 'temjperature, have led to the belief that operation at high temperatures, suchas'that of or resulting from the steaming of theimpregnated fabric, would be impractical. y

I have made the surprising discovery that the full advantages of increased operating temperatures with respect to speeding up th bleaching reaction may be attained without the disadvansolution such as is retained by the textilejaft'er immersion in and removal from a bath of the solution or such as results, for: in'stance,"from immersing'the textile in the-solution and remov' ing excess solution therefrom, as by draining or passing between squeeze rolls.

Impregnation of the textile with the solution may be accomplished by immersion, padding, spraying, or other procedure which assures reafsonably thorough wetting; Thereafter excess so}- lution, if any, is drained or squeezed r o ure particularly where good absorbency is desired. Prior to the treatment of thetextile with the By subjecting the unfinished textiletoa caustic steaming, washing in hot or cold water, and then steaming the textile whileii-mpregnated with'ran. aqueous solution of hypochlorite:andmhloritezand again washing, superior results have been obtained with respect to whitenessee pellent. and. uniform absorbency, susceptibility to dyeing end.

freedom from motes and the like.

Particularly desirable results are obtained bypag nation; :in order: tolobtaini satisfactory; uni?- 7 form absorbency. When using the-ztwcwstep :cp-

.emtion'of nay-present.-inventionaonlyone-caustic :etcsmine iseusually required: :efiects asub- .etential; economrt n rfinishin opera ionsand apwfpfifllsfitoibe(111 324 he. effecting of further; sub- ,siaintial ,scourinssaction in thesecond, :01: bleach.-

- inglstase crane-process. 1"

- Therwashinggof. thetextil'eiollowing; the caustic .steamingia'and ;alsofollowing the chlorite hy por- .chlor-ite steaming-l; operation; may,;becarriedout however, washing in hotlwaterzhas been found to giye-i-mproved results...

In carrying out theefirstistep 10f theoperati'on, thetextileoisimmersed in, :or otherwise wetwith .theicaustic; solution; preferably hot: and; con-tame lingga :penetranta About. 0. l.-% of the :penetrant: is .usuallw suflicient, although greater or evenzlesser amounts of;thepenetrants may beused; depend- --ing-.primanily; upon a the nature lief the, textile. Antes-impregnation anywsurplus solution-,is;;prefemhly; =removed from thezetextile :as; by, draining ormildsqueezinegbetweenrollers;1- I Thecaustic: impregnated :cloth thenpassed into contact .with steam,- -.either-;at,-rull width! or in rope-form: For-instance, the ltex-tilemay-be passed at full widthethrough;aasteamschamber wherein it"is subjected to anatmosphere of steam for-a lperiod-ofvtime sufiicient toscour the textile, ionthei textile! inirope form may belrapidly heated by. agbrief contact. with [steam .andlthen :stored in bulkiinla chamber or, pit where it isrkept hot; for the desired period withoutefurther introduction of steamzn Steamingtime, .concentrationofithc caustic so- "lutioneand temperature;-: are to a considerable ex.-

tent. -,interdependent.- Particularly; 3 advantageous .results. are I. obtained when the {concentration of -theecausticasolutionl is .about. 3%". or greater. by

weight, .say 3 to 7 and ..the -,textile, impregnatedstherlewith .is. subjected etc. ,steam sat. at.-

vmoshheriu pressure for a.period-suificientto-permit the textile to assume approximately the temperature of the steam, and the hot textile is thereafter stored in a pit for about 1 hr. These operating conditions are, however, subject to considerable variation.

After the caustic steaming, the textile is washed and; preferably immediately,-iS- subjected to the second: stage; i. e., thehypochlorite-chlorite steaming operation. Instead of the caustic lipsteaming, the textile may, in accordance with the broader aspect of this invention, as previously noted-be subjected to other conventional scouri-ng operations.-for --instance, kiering, but in order toeattainthe fullgbenefits of the present invention, the .:textile should be subjected to a caustic steaming and washing immediately preceding the herein described step of the process comprising the steaming, while impregnated with the hypochlorite-chlorite solution.

The steaming of the textile while impregnated with the hypochlorite-chlorite solution may likewise-be carried out: inany conventional steamer. either .at full width or in-:rope :iormnin which the impregnated itextile'; :is. subjected to. the-e10.- vated temperature for a sufficient-period-toiaccomplish the desired extent oflbleaching.

Particularly desirable- :resultsthaveebeenaobtained' in bleaching textile in rope. :form by PISS? ing. theiimpregnated textile-through a .J-chute having: perforations. near the lower end. of l the longlegof the chute, .saidoperiorations ,beinz connectedwith a source. of steam, .as. by-a Jacket welded onto the. outside wall of. the. chute ancienclosing {the periorations. In this apparatus steam is. injected into the J-chute through the petiole..- tions and the textile, as,.it;.passes. throughthe J-chute, in-the conventional manner, is gradually heated to. approximately thesteam temperature as. it movesqdownwardly ,through. thelong: leg ,of the chute toward .the point. .of steam; injection, and. .is thereafter subjected ,to :the. damp, temperature environment until it. has .been with, drawn fromv the shorter. leg .of. theJ-chute.

In. this operation, also, thezeconcentratioh .oi ,the impregnating solution, temperature andtime factor. are interdependent, .and each .maybe varied. over a considerable range; :suitable.,c0m. pensation being made with respect to the other conditions. Optimum. operating conditionshre alsodependent upon theextent ofableachingrequired and the condition of. the .textfle. Generally, satisfactory results have been -.obtained by maintaining the impregnated textile. :at an average temperatureof rabout 140,.to F. forna period of. about- 1 hr,., .for instance while passing through a J-chute-such as just descrlbed andinpjecting through the perforation :into the J-chute atmospheric-pressure steam, the ratio of hypochlorite -eto wchlorite the impregnating-solu- .tion. being about .1.5,.to. 1,- based on available chlorine and said: solution containing; about 2.5 to-.3 grams of. available chlorine.per. liter;

Thetime'factor may be varied by yaryinglthe rate at which the textile is -passed-.through- -the .steamingzone, that of the. above-described J- chute; for-instance, or. by'-.varying-;- the lengthiof the steaming zone. A satisfactory. bleach I i is usually obtained .in about z /e .to-nabout 1 hr.,- depending primarily upon the I temperature employed.

This increased rate -.of bleaching isunade possible. .by my surprising ,discovery ,that by follmv ing the procedure herein-described, the. temperae ture at which the bleaching fies-effectednnay ex-e .ceed ..100 F. without. deleteriously affecting the textile, without causing excessive evolution of chlorine dioxide and without causing such rapid depletion of the hypochlorite as to render the process impractical. According to our present process, the textile impregnated with the hypochlorite-chlorite solution may be heated to temperatures approaching that of steam at atmospheric pressure, i. e., 212 F. thus speeding up the bleaching reaction with beneficial results, with respect to economy in time and improved whiteness and absorbency of the textile.

The ratio of hypochlorite to chlorite and the available chlorine concentration and pH of the solution are also subject to considerable variation. The ratio of hypochlorite to chlorite may. with advantage, be varied Within the range of about 0.51:1 to about 4:1, based on available chlorine, the optimum ratio depending largely upon other operating conditions and the results desired. Rapid and satisfactory bleaching has generally been obtained where the available chlorine concentration of the impregnating solution is about 2.5 to 3 grams per liter. The pH of the solution should not be less than 7 and is desirably within the range of about 9 to 11.

As previously noted, it is frequently desirable to subject the textile to a scouring operation prior to steaming the textile impregnated with the chlorite-hypochlorite solution. It will be understood that in carrying out such two-step operation, the textile may, if desired, be subjected to an intervening souring.

I claim:

1. In the bleaching of cellulosic textiles by treating the textile with an aqueous solution of a chlorite activated by the presence of a hypochlorite and having a pH not less than 7, the improvement which comprises efiectin bleaching of the textile with said solution at a temperature in excess of 100 F. without appreciably diminishing activation of the chlorite by decomposition of the hypochlorite, said bleaching being effected by impregnating the textile with said solution and steaming the impregnated textile in the presence of only so much of the solution as is retained in the textile, for a period of time sufficient to efiect the desired bleaching.

2. In the bleaching of cellulosic textiles by treating the textile with an aqueous solution of a chlorite activated by the presence of a hypochlorite and having a pH not less than 7, the improvement which comprises effecting bleaching of the textile with said solution at a temperature in excess of 100 F. without appreciably diminishing activation of the chlorite by decomposition of the hypochlorite, said bleaching being effected by impregnating the textile with said solution and steaming the impregnated textile in the presence of only so much of the solution as is retained in the textile, for a period of time suflicient to effect the desired bleaching, the ratio of the hypochlorite to chlorite in the solution being within the range of about 0.5:1 to about 4:1.

3. In the bleaching of cellulosic textiles by treating the textile with an aqueous solution of a chlorite activated by the presence of a hypochlorite and having a pH not less than 7, the im provement which comprises effecting bleaching of the textile with said solution at a temperature in excess of F. without appreciably diminishing activation of the chlorite by decomposition of the hypochlorite, said bleaching bein effected by impregnating the textile With said solution, heating the impregnated textile, in the presence of only so much of the solution as is retained in the textile, by contact with steam, and maintaining the textile at a temperature Within the range of about 100 F. to about 212 F. for a period of time sufficient to effect the desired bleaching.

4. In the finishing of cellulosic textiles, the process which comprises impregnating the textile with an aqueous solution of caustic soda, steaming the impregnated textile, washing the textile and thereafter impregnating the textile with an aqueous solution of sodium chlorite activated by the presence of sodium hypochlorite and having a pH not less than 7, and effecting bleaching of the textile with said solution at a temperature in excess of 100 F. without appreciably diminishing activation of the chlorite by decomposition of the hypochlorite, said bleaching being effected by heating the impregnated textile, in the presence of only so much of the chlorite-hypochlorite solution as is retained in the textile, by contact with steam, and maintaining the textile at a temperature within the range of about 100 F. to about 212 F. for a period of time sufiicient to eifect the desired bleaching.

RALPH L. CARR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Clark Feb. 4, 1936 Kauffman 1. Feb. 6, 1940 Hundt Mar. 19, 1940 Campbell Dec. 30, 1941 Campbell Nov. 9, 1943 MacMahon Sept. 26, 1944 Vincent Aug. 28, 1945 FOREIGN PATENTS Country Date France July 28, 1925 Great Britain Apr. 14, 1943 Great Britain Apr. 21, 1943 Great Britain June 7, 1944 OTHER REFERENCES Number Number 

1. IN THE BLEACHING OF CELLULOSIC TEXTILE BY TREATING THE TEXTILE WITH AN AQUEOUS SOLUTION OF A CHLORITE ACTIVATED BY THE PRESENCE OF A HYPOCHLORITE AND HAVING A PH NOT LESS THAN 7, THE IMPROVEMENT WHICH COMPRISES EFFECTING BLEACHING OF THE TEXTILE WITH SAID SOLUTION AT A TEMPERATURE IN EXCESS OF 100*F. WITHOUT APPRECIABLY DIMINISHING ACTIVATION OF THE CHLORITE BY DECOMPOSITION OF THE HYPOCHLORITE, AND BLEACHING BEING EFFECTED BY IMPREGNATING THE TEXTILE WITH SAID SOLUTION AND STEAMING THE IMPREGNATED TEXTILE IN THE PRESENCE OF ONLY SO MUCH OF THE SOLUTION AS IS RETAINED IN THE TEXTILE, FOR A PERIOD OF TIME SUFFICIENT TO EFFECT THE DESIRED BLEACHING. 